The communication accuracy between a transmitter and receiver in a wireless communication network increases if the receiver can accurately estimate the channel, i.e., the signal propagation path(s) between the devices. Channel estimation is typically based at least in part on recovering known pilot symbols. For the uplink, Universal Mobile Telecommunications System (UMTS) specifies a Dedicated Channel (DCH) and an Enhanced Dedicated Channel (E-DCH), both corresponding to a set of separate channelization codes for data and associated control signaling. The number of data codes carrying the E-DCH and the spreading factors depend on the data rate used. An E-DCH Dedicated Physical Data Channel (E-DPDCH) carries the E-DCH transport channel. An E-DCH Dedicated Physical Control Channel (E-DPCCH) carries the control information associated with the E-DCH. Particularly, the E-DPCCH carries information of the transport block format (e.g., E-TFCI symbols), information for Hybrid Automatic Repeat-reQuest (ARQ) and scheduling. The control channel DPCCH carries the pilot and control symbols. The E-DPDCH and E-DPCCH channels may be multiplexed with the data channel (DPDCH) of the DCH which uses a 10 ms Transmission Time Interval (TTI) for circuit switched services.
As part of the High-Speed Packet Access (HSPA) evolution, higher order modulation schemes and higher data transmission rates are being implemented. Higher order modulation schemes such as 16QAM (Quadrature Amplitude Modulation) and above invariably result in reduced symbol spacing. Improved channel estimation is needed when higher order modulation is employed because symbol detection becomes more difficult when symbol spacing is reduced. Besides using the DPCCH symbols for channel estimation, channel estimation accuracy may be improved by using E-DPCCH symbols. At high data rates, E-DPDCH uses a high order modulation and is transmitted at high power. Conventional systems do not scale the power level of the DPCCH and E-DPCCH with respect to the data transmission rate. Accordingly, the symbols transmitted over the DPCCH and E-DPCCH become unreliable when higher-order modulation is used because the DPCCH and E-DPCCH symbols are drowned-out by the high power E-DPDCH. As such, the DPCCH and E-DPCCH cannot be used to obtain accurate channel estimates over a broad range of data transmission rates.